Abstract: This paper presents an analysis of the hydraulic model of the slope instability of a down-dipping soft sandwich slope, focusing on the southern slope landslide project of Fushun west open pit mine. The study investigates the effects of groundwater and rainfall infiltration on the slope deformation evolution process using numerical simulation analysis with FLAC^3D software. The sliding law of the slope with soft interlayer under the action of groundwater and rainfall infiltration is summarized. The results show that rainfall infiltration and groundwater flow produce osmotic pressure on the slope, causing the development of a large number of rupture surfaces on the slope. The maximum cumulative displacement is about 1.27 m resulting in a multi-stage landslide with a mixed landslide type. During the deformation and failure of the slope, tension failure is prone to occur along the weak layer near the slope top, providing a channel for surface water infiltration and groundwater migration, and showing the characteristics of multiple sliding surface, forming a continuous shear failure surface, which further leads to the multi-stage deformation of the slope. Under the influence of groundwater and rainfall infiltration, the water content in the weak layer of slope accumulates, resulting in damage and rupture, reducing the volume strain increment, lowering the effective stress, increasing the pore pressure, and reduing the shear strength, thereby inducing landslide. To improve the stability of the slope, the study compares different prevention and control schemes, including backfilling presser foot with different slope heights. The study finds that compared with the rainfall condition, the slope protected by backfilling presser foot with different slope heights has a higher safety factor. Considering the engineering practice, the backfilling and pressure protection up to half of the slope height has a better effect on preventing and controlling the slope, and the slope is more stable.